Recently, it has been tried to add a unique identifier to each material data including video and audio data obtained by video and audio recording, etc. in order to identify the material data. Such an identifier is proposed as UMID (unique material identifier) in SMPTE (Society of Motion Picture and Television Engineers)—330M.
The above-mentioned UMID is an identifier which is to be added to material data being created and unique over the world. It will not be used in common to more than one material data. Also, a new identifier is added to a copy of material data. Even in case a complete package formed from a plurality of material data is created, UMID allows to know who owns the copyright of each material data from the complete package and thus protect the copyright for each material data. Also, UMID can be used as an effective index for searching material data including many copies thereof for original material data. Actually at a broadcast station or the like, identification of material data by UMID makes it possible to make clear which one of the material data is being used in which one of a series of processes such as recording, creation, edition, transmission and archiving, and it is made possible by linkage between metadata as additional data about video and audio data and the video and audio data by UMID to know how each material data is at the present and how it has been used.
UMID having been described above has a structure as shown in FIG. 1. As shown, UMID is an Extended UMID including a total of 64 bytes and which consists of a 32-byte Basic UMID used for identification of material data (this identification is the primary function of UMID) and a 32-byte Signature Metadata used for identifying the material data according to the contents of them.
As a simple identifier, the basic UMID can be used to identify material data (this is the primary function of UMID). However, the basic UMID is formed from random information generated for the identification of material data but does not contribute to any intuitive recognition of material data. Material data can be identified according to when, where and by whom it was created, for example, and the contents of the material data can easily be recognized intuitively. On the basis of this fact, the extended UMID format is defined by such information added as Signature Metadata to the basic UMID. Such a UMID allows to make a linkage between video and audio data and metadata about the video and audio data in order to identify the material data.
As shown in FIG. 1, the Signature Metadata in the aforementioned UMID has a 12-byte Spatial Coordinates area. In this Spatial Coordinates area, position information about where the material data were created is stored as altitude, longitude and latitude information. These pieces of position information stored in the Spatial Coordinates area are based on values measured by a global positioning system (GPS) when recording the material data, for example.
More particularly, the Spatial Coordinates area consists of data areas for 4-byte altitude information, 4-byte longitude information and 4-byte latitude information, respectively, as shown in FIG. 2. Each of these pieces of position information is given in 2-digit binary coded decimal (BCD) notation per byte. Therefore, in the Spatial Coordinates area, the altitude information can be stated with a value from 0 to 99999999 m, for example.
Definition of a position on the earth by an altitude, longitude and latitude will be described herebelow. To define a position on the earth, a reference plane will be determined and the position be defined in the reference plane since the earth's terrain is rough. Generally, an ellipsoid of revolution resembling closely the so-called geoid is regarded as representing the terrain shape. The ellipsoid of revolution is called “earth ellipsoid”. A position on the earth is defined by an altitude, longitude and latitude on the basis of the earth ellipsoid.
Various earth ellipsoids have been proposed, and each of the countries defines a geodetic coordinate system and an earth ellipsoid from its own point of view. In the positioning by the aforementioned GPS, the so-called world geodetic system—84 (will be referred to as “WGS-84” hereunder) coordinate system is used as the geodetic coordinate system. The WGS-84 coordinate system is very like to the international terrestrial reference frame (ITRF) coordinate system which is currently regarded as the most accurate geodetic coordinate system. It is a coordinate system taking the earth as the center thereof as in the ITRF coordinate system.
More detail explanation will be made herebelow by assuming an earth ellipsoid EE as shown in FIG. 3 and defining the position of a point A on the basis of the earth ellipsoid EE. It should be noted that in FIG. 3, the coordinate axes of a three-dimensional orthogonal coordinate system is defined as taking the center of gravity C of the earth ellipsoid EE as the origin of the coordinate system, with the x axis being extended toward an intersection between the so-called Greenwich Meridian GMR and equator EQ, y axis being extended toward the east longitude of 90 deg. and with the z axis being extended toward the north pole. In this case, the latitude of the point A is given as an angle φLA formed between a normal line N depending vertically from the point A to the surface of the earth ellipsoid EE and equatorial plane EQS. Further, the longitude of the point A is given an angle φLO formed between the meridian MR passing through an intersection I between the normal line N and surface of the earth ellipsoid EE and the Greenwich meridian GMR. Also, the altitude of the point A is given as a distance h from the point A to the point (intersection) I. Even when the point A is actually on the earth, it is given as a negative value when it is lower than the surface of the earth ellipsoid EE. In the positioning by GPS, the altitude, longitude and latitude of an arbitrary point on the earth are determined similarly to the point A.
The altitude information stored in the Spatial Coordinates area in UMID is defined as a distance from the center of the earth. That is, in the geodetic coordinate system indicated by the earth ellipsoid EE in FIG. 3, the altitude information is stated as a distance from the center of gravity C. For easier understanding, a section, taken by the meridian MR, of the earth ellipsoid EE is assumed to be as shown in FIG. 4. As known from FIG. 4, the altitude of the point A measured by GPS is given as a distance h from the point A to the point I, while the altitude information stored in the Spatial Coordinates area is stated as a distance r from the point A to the center of gravity C.
Therefore, the apparatus which generates UMID has to convert altitude information acquired using a GPS receiver into a distance from the center of gravity of the earth before storing the altitude information into the Spatial Coordinates area. However, the altitude information stated as the distance r is not any value which can be known intuitively, and evidently it is not practical.